#include<iostream>
using namespace std;
struct mon_hoc
{
          float diem;
          float he_so;
};
float dtc( float a)
{
       if(a<0) return -1;
       if(a>=0&&a<4) return 0;
       if(a>=4&&a<=5.4) return 1;
       if(a>=5.5&&a<=6.9) return 2;
       if(a>=7&&a<=8.4) return 3;
       if(a>=8.5&&a<=10) return 4;
       if(a>10) return -1;
}
float kt_heso(float b)
{
         if(b<=0) return -1;
         if(b>0) return 1;
}
int xep_loai(float c,float d)
{
       if(c<1) cout<<"Ban bi buoc thoi hoc"<<endl;
       if(c>=1&&c<2)
       {
                    cout<<"Ban xep loai: Yeu"<<endl;
                    if(d>0)cout<<"Ban phai thi lai "<<d<<" mon"<<endl;
       }
       if(c>=2&&c<2.5)    
       {
                       cout<<"Ban xep loai: Trung binh"<<endl;
                       if(d>0)cout<<"Ban phai thi lai "<<d<<" mon"<<endl;
       }
       if(c>=2.5&&c<3.2)    
       {
              if(d==0)cout<<"Ban xep loai: Kha"<<endl;
              else cout<<"Ban xep loai trung binh vi thi lai "<<d<<" mon"<<endl;
       }
       if(c>=3.2&&c<=4)    
       {
                        if(d==0)cout<<"Ban xep loai: Gioi"<<endl;
                        else cout<<"Ban xep loai trung binh vi thi lai "<<d<<" mon"<<endl;
       }        
}
int main()
{
       int n;
       cout<<"Moi ban nhap vao so mon hoc: n=";cin>>n;
       cout<<"--------------------------------------------------------"<<endl;
       mon_hoc mon[n];
       cout<<"Hay nhap vao diem, va he so cua tung mon:"<<endl;
       for(int i=0;i<n;i++)
       {
               cout<<"Mon "<<i+1<<":"<<endl;
               cout<<"Diem mon "<<i+1<<"="; cin>>mon[i].diem;
               cout<<"He so mon "<<i+1<<"=";cin>>mon[i].he_so;
       }
       float tong_diem=0;
       float tong_he_so=0;
       int loi=1;
       int dxl=0;
       for(int i=0;i<n;i++)
       {
               if(dtc(mon[i].diem)==0) dxl++;
               if(dtc(mon[i].diem)==-1)    
               {
                   cout<<"Xin moi ban xem lai doi chut, co the ban da nham trong qua trinh nhap diem"<<endl;
                   loi=-1;
                   break;
               }
               else
               {
                    if(kt_heso(mon[i].he_so)==-1)    
                    {
                            cout<<"Xin moi ban xem lai doi chut, co the ban da nham trong qua trinh nhap he so"<<endl;
                            loi=-1;
                            break;
                    }
                    else
                    {
                        tong_diem=tong_diem+dtc(mon[i].diem)*mon[i].he_so;
                        tong_he_so=tong_he_so+mon[i].he_so;
                    }
               }
       }
       cout<<"-------------------------------------------------------------------"<<endl;
       float dtk;
       if(loi!=-1)    
       {
                   dtk=tong_diem/tong_he_so;
                   cout<<"Diem tong ket tin chi cua ban la: "<<dtk<<endl;
                   xep_loai(dtk,dxl);
                   cout<<endl;
       }
       system("pause");
}